1. Field of the Invention
The present invention relates to a method for producing a conjugated diolefin and an apparatus for the production.
2. Description of the Related Art
Conjugated diolefins, such as 1,3-butadiene (hereinafter, also referred to simply as “butadiene”) and isoprene, are industrially produced from a naphtha pyrolysis hydrocarbon mixture based on a separation purification/recovery method by extraction or extractive distillation, and are used as raw materials for synthetic rubber, resin and the like. According to the Japanese Industrial Standards (JIS K 1533-1980), the purity of butadiene is defined as 98.0% or more. Thus, when butadiene or isoprene is used as an industrial raw material, a high purity is demanded. The reason for this is that when producing synthetic rubber, resin and the like by polymerizing butadiene or isoprene that contains impurities, the impurities could inhibit polymerization of the butadiene or isoprene or cause the polymerization to proceed excessively, causing the physical properties of the obtained synthetic rubber, resin and the like to deteriorate.
Conventionally, a separation purification method of a naphtha pyrolysis product has been employed for industrial butadiene production. Impurities that are known to be produced in this method include acetylenes and carbonyl compounds. However, these are sufficiently removed by extractive distillation using a polar solvent, such as N,N-dimethylformamide (DMF). The resultant product is used as a raw material for synthetic rubber, resin and the like by purifying until it satisfies the standard.
In addition to naphtha pyrolysis, other known methods to produce butadiene and isoprene include catalytic oxidative dehydrogenation of n-butene or isopentene. This method is known to produce, other than the target butadiene and isoprene, various reaction byproducts, such as organic acids, aldehydes, and compounds with high boiling point, that cannot be produced in a naphtha pyrolysis method, because this method employs an oxidation reaction in which oxygen is involved. Some of these byproducts are present in the product gas as fine solid particles. Patent Document 1 describes a method in which butadiene produced using, for a raw material, BBSS (a mixture mainly of hydrocarbons having 3 to 5 carbon atoms), which is obtained by separating butadiene and isoprene from a C4 fraction obtained by naphtha pyrolysis, is purified by setting the concentration of acetylene-based hydrocarbons in the product gas to a specified level or less, quenching the resultant product gas with cooling water, recovering the product in a solvent such as DMF, and then performing extractive distillation. Further, Patent Document 2 describes a method in which a product gas by reaction containing butadiene obtained by catalytic oxidative dehydrogenation of n-butene is sent to a quenching tower, and a byproduct with high boiling point mainly composed of organic acids is removed by dissolving in an aqueous phase by charging an alkali into the chilled water to be fed to the top of the quenching tower. In addition, Patent Document 2 also describes providing a scrubber at the outlet of the quenching tower to trap the solid particles produced as byproducts.